The present invention relates to a titanium laminate or a titanium composite material having a multilayered structure which comprises a titanium sheet or a titanium alloy layer and a layer of a macromolecular material.
Since titanium and an alloy comprising mainly of titanium (hereinafter referred to as xe2x80x9ctitanium materialxe2x80x9d) have inherent excellent properties such as lightweight property, high strength (high specific strength) and high corrosion resistance, titanium materials are used in various fields for applications not only as industrial materials such as fuselage materials and component materials for aircraft, materials for heat exchangers and electrode materials, but also as building materials such as roof materials and wall materials, and materials for goods of livelihood such as materials for decoration articles, sporting goods and equipment for leisure time amusement.
However, titanium materials are expensive compared with other materials for use (e.g. about 10 times higher in cost than stainless steel generally used as a corrosion-resistant material) and are poor in processability. For these drawbacks, titanium materials are not replacing other materials and unlikely to be used in increasing amounts despite their excellent properties as described above.
To reduce the costs of expensive titanium materials, an attempt was made to provide a xe2x80x9ccomposite materialxe2x80x9d which comprises an inexpensive material covered with a thin sheet of titanium material by means of a metallurgical or mechanical process. The attempt was partly realized for commercial products.
However, it is impossible to form a coating layer of titanium material on the surface of other materials by an inexpensive wet plating method such as an electroplating method. Consequently a layer of titanium material has been conventionally provided by making a composite laminate using a dry plating process such as PVD, CVD or the like or a cladding method.
For example, in the case of PVD, a titanium material is vaporized under a high vacuum and is deposited on to the surface of a target substrate to form a coating film. However, the PVD has a drawback of being carried out at a high temperature of 100 to 200xc2x0 C., whereby substrates are limited to those having resistance to high-temperature heat.
The CVD is conducted by heating a material containing a titanium to chemically react the material with a substrate, thereby forming a coating film on the substrate. Thus, the CVD process employs a higher temperature ranging from about 500 to about 700xc2x0 C. than the PVD process, and has a drawback that a titanium material can be applied only to a substrate having high heat resistance.
Further, both of PVD and CVD require large-size equipment to obtain a coated material suited for practical use. Consequently these methods entail drawbacks that a substrate to be coated with titanium is inevitably limited in shape and size, thereby increasing the costs of a composite material.
The cladding method intended to give a laminated composite material is advantageous over the PVD and CVD in that the cladding eliminates needs for a high vacuum device required by the PVD and for a reaction device required by the CVD. But the cladding necessitates the formation of a titanium film of greater thickness than required in order to metallurgically or mechanically bond the titanium material to a substrate of other metals. Moreover, the cladding process has further drawbacks of requiring large-scale, powerful production equipment and ntails a difficulty in small-lot production, resulting in an increase in costs for composite materials.
Japanese Examined Patent Publication No.225851/1996 discloses a technique for xe2x80x9cpreventing the deposition of marine foiling organism on ships or offshore structures made of fiber-reinforced plastics (FRP) by applying titanium, zirconium, tantalum, niobium or an alloy containing chiefly any of them with an adhesive to a portion of the ship or offshore structure in contact with seawater.xe2x80x9d The disclosed technique can effectively prevent the deposition of oceanic organisms, but the technique has a drawback. A titanium material has a noticeable spring-back characteristic compared with stainless steel and the like. Accordingly spring back is brought about by the titanium sheet after coating the FRP substrate with the titanium material, making it likely to induce peel between the titanium sheet and the adhesive layer satisfactorily bonded to the FRP substrate.
For the reason, among others, that a titanium composite material has a much higher affinity with oxygen than other metals, a stable passive state film of titanium oxide is invariably formed on the surface of titanium material. Consequently it is difficult to maintain a firm bond at an interface between the adhesive and the titanium material due to the formed oxide film. From a practical viewpoint, a great difficulty is encountered in preparing a composite material of high performance by bonding a titanium material to a macromolecular material with an adhesive.
A principal object of the present invention is to provide a novel technique for practical use in various fields of a titanium material having excellent properties at a low cost.
The present inventors conducted extensive research, directing attention to the foregoing state of the art and found the following. Use of a thin sheet or foil of titanium material (hereinafter referred to simply as xe2x80x9ctitanium sheetxe2x80x9d or xe2x80x9ctitanium alloy sheetxe2x80x9d), which was not used in conventional composite materials, results in an inexpensive, useful, novel composite material, when the surface of the titanium sheet is treated for property modification and the treated titanium sheet is bonded to a macromolecular material with an adhesive.
The present invention provides the following titanium composite materials.
1. A titanium composite material comprising a bonded laminate having a layer of macromolecular material bonded to the modified surface of a titanium sheet or a titanium alloy sheet.
2. The titanium composite material as defined in item 1, wherein the titanium sheet or the titanium alloy sheet has a thickness of 0.1 to 500 xcexcm.
3. The titanium composite material as defined in item 2, wherein the titanium sheet or the titanium alloy sheet has a thickness of 1 to 50 xcexcm.
4. The titanium composite material as defined in any of items 1 to 3, wherein the layer of macromolecular material is formed of a thermosetting resin or a thermoplastic resin.
5. A process for preparing a titanium composite material, the process comprising the step of bonding a macromolecular material to a titanium sheet or a titanium alloy sheet having a modified surface to be bonded.
6. The process as defined in item 5, wherein the modified surface of the titanium sheet or titanium alloy sheet to be bonded has substantially no passive state film thereon.
7. The process as defined in item 6, wherein the modified surface of the titanium sheet or the titanium alloy sheet to be bonded is one from which a passive state film has been removed by etching.
8. The process as defined in item 6, wherein the surface of the titanium sheet or titanium alloy sheet to be bonded is modified by removing the passive state film with hydrofluoric acid.
9. The process as defined In item 5, wherein the modified surface of the titanium sheet or titanium alloy sheet to be bonded is one which is coated with a primer.
10. The process as defined in item 9, wherein the primer is a coupling agent.
11. The process as defined in item 10, wherein the coupling agent is of the titanate type having an unsaturated bond in the side chain.
12. The process as defined in item 5, wherein the modified surface of the titanium sheet or titanium alloy sheet to be bonded is one which is treated for preventing the re-formation of passive state film thereon after removal of the passive state film therefrom by etching.
13. The process as defined in item 12, wherein the treatment for preventing the re-formation of passive state film is a dipping treatment using a reducing agent.
14. The process as defined in item 13, wherein the reducing agent is an aqueous solution of formic acid.
15. The process as defined in item 10, wherein the treatment for preventing the re-formation of passive state film is an electrolytic reduction treatment in the presence of cathodic polarization.
16. The process as defined in item 15, wherein the current density in the electrolytic reduction treatment is not lower than 0.5 A/dm2.
17. The process as defined in item 16, wherein the current density is in the range from 1 to 50 A/dm2.
18. The process as defined in item 5, wherein the modified surface of the titanium sheet or titanium alloy sheet to be bonded is one which is coated with a primer after treatment for preventing the re-formation of passive state film following the removal of passive state film by etching.
19. The process as defined in item 5, wherein the titanium sheet or titanium alloy sheet has a thickness of 0.1 to 500 xcexcm.
20. The process as defined in item 5, wherein the titanium sheet or titanium alloy sheet has a thickness of 1 to 50 xcexcm.
21. The process as defined in item 5, wherein the layer of macromolecular material is formed of a thermosetting resin or a thermoplastic resin.
22. The process as defined in item 5, wherein a thermosetting resin is bonded with an adhesive to the titanium sheet or titanium alloy sheet having a modified surface to be bonded.
23. The process as defined in item 22, wherein the thermosetting resin is bonded to the titanium sheet or titanium alloy sheet using an acrylic resin-type or butyl rubber-type tackifier.
24. The process as defined in item 5, wherein a melt of a thermoplastic resin is press-bonded to the titanium sheet or titanium alloy sheet having a modified surface to be bonded.